According to the model of Knudson for tumorigenesis (Cancer Research, vol. 45, p. 1482, 1985), there are tumor suppressor genes in all normal cells which, when they become non-functional due to mutation, cause neoplastic development. Evidence for this model has been found in the cases of retinoblastoma and colorectal tumors. The implicated suppressor genes in those tumors, RB and p53 and DCC, were found to be deleted or altered in many eases of the tumors studied. (Hansen and Cavenee, Cancer Research, vol. 47, pp. 5518-5527 (1987); Baker et al., Science, vol. 244, p. 217 (1989); Fearon et al., Science, vol. 247, p. 49 (1990).)
In order to fully understand the pathogenesis of tumors, it will be necessary to identify the other suppressor genes that play a role in the tumorigenesis process. Prominent among these is the one(s) presumptively located at 5q21. Cytogenetic (Herrera et al., Am J. Med. Genet., vol. 25, pg. 473 (1986) and linkage (Leppert et al., Science, vol. 238, pg. 1411 (1987); Bodmer et al., Nature, vol. 328, pg. 614 (1987)) studies have shown that this chromosome region harbors the gene responsible for familial adenomatous polyposis (FAP), an autosomal-dominant, inherited disease in which affected individuals develop hundreds to thousands of adenomatous polyps, some of which progress to malignancy. Additionally, this chromosomal region is often deleted from the adenomas (Vogelstein et al., N. Engl. J. Med., vol. 319, pg. 525 (1988)) and carcinomas (Vogelstein et al., N. Engl. J. Med., vol. 319, pg. 525 (1988); Solomon et al., Nature, vol. 328, pg. 616 (1987); Sasaki et al., Cancer Research, vol. 49, pg. 4402 (1989); Delattre et al., Lancet, vol. 2, pg. 353 (1989); and Ashton-Rickardt et al., Oncogene, vol. 4, pg. 1169 (1989)) of patients without FAP. Thus, a putative suppressor gene on chromosome 5q21 appears to play a role in the early stages of colorectal neoplasia in both sporadic and familial tumors. However, no gene has been identified on 5q21 which is a candidate suppressor gene. Thus there is a need in the art for investigations of this chromosomal region to identify genes and to determine if any of such genes are associated with the process of tumorigenesis.